Mussels’ sticky feet lead to applications

The remarkable adhesive powers of the mussel are being harnessed for diverse applications, ranging from medical adhesives to climate-change research.

J. Herbert Waite was a graduate student in biochemistry in the 1970s when he began to wonder how mussels cling to rocks in the turbulent intertidal zone, where they slurp nourishing plankton from the water. So in summers and fall, Waite donned Wellington boots and rubber gloves and headed for the Connecticut shore near Rocky Neck State Park to pluck bivalves from the water.

Despite initial skepticism from his peers about the research, Waite is now considered a pioneer in the field of bioadhesives, a thriving interdisciplinary endeavor that connects marine biology to materials science. “Nature is a bottomless treasure trove, as far as adhesion strategies go,” says Waite, now at the University of California at Santa Barbara. “Adhesion is often a survival mechanism, but to my surprise very few strategies are the same. Barnacles and mussels have completely different strategies, different architectures.”

Gas Attack

The mussel’s protein glue may be tough, but it has an Achilles’ heel: acid. That makes the mussel vulnerable to the effects of climate change.

The growing quantities of carbon dioxide in the atmosphere are also dissolving in the oceans to create carbonic acid. As a consequence, average ocean pH has dropped from 8.2 to 8.1 in the past 100 years. The Intergovernmental Panel on Climate Change estimates that it could drop by another 0.3 or 0.4 pH units before the end of the century (10). Laboratory studies on marine organisms suggest that many species could face a dramatic decline as the pH continues to drop. Acidic seas tend to have a low concentration of carbonate ions, for example, which shellfish use to build their shells.

Acidification is also bad for byssal threads, says marine biologist Emily Carrington at the University of Washington in Seattle. “The fibers are extrusions of mussels, not unlike our hair,” she says. “If you’re nutritionally stressed, one of the first things that happens is your hair falls out.” She believes that dramatic declines in mussel populations, as in other organisms, could be a bellwether for how vulnerable coastal ecosystems are reacting to ocean acidification. Her research has already shown that byssal threads change on seasonal cycles, becoming stronger in the winter and weaker in the summer. Carrington is now trying to pin down how ocean chemistry and temperature affect those cycles.

In laboratory experiments, Carrington has been testing the strength of byssi in water with different concentrations of carbon dioxide. As the researchers ratcheted the carbon dioxide load in the water, the pH dropped from 8.0 to 7.5, within the range found in commercial mussel beds. However, at pH 7.5, individual threads began to break at shorter extensions under smaller loads. In June, the researchers reported that this was caused by a breakdown in protein cross-linking rather than a loss of adhesion (11). For wild mussels, that could mean they are unable to attach to rocks in water that is too acidic.

Monitoring mussels’ sticking power could help researchers develop better models of how climate change will affect complex coastal ecosystems, says Carrington; most ocean acidification models currently focus on the open ocean. A better understanding of how mussels respond to water chemistry could also improve the mussel aquaculture industry, which was worth $1.5 billion in 2009. Mussel farms, where mussels are grown in dense clusters on long underwater ropes, could use Carrington’s research to tweak the temperature, composition, and flow of water pumped through the hatchery.

The study of bio-adhesion has come a long way since Waite’s first mussel-gathering trips. The humble mollusc is joining together disparate fields, promoting fruitful interdisciplinary science with potentially important applications. “It’s very gratifying for those us that started as biologists,” says Waite.

Stephen Ornes, Proceedings of the National Academy of Sciences of the United States of America 2013 110(42): 16697-16699. Full article.


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